The invention relates to a traction motor in vehicles with an electric or diesel-electric drive, the traction motor which is mounted in a housing being grounded.
In vehicles of the generic type, the traction motors are fed either directly from a power system or via a converter with electronic power actuating elements. The housings of the traction motors are grounded here via a grounding cable in the vehicle with an electric drive. Owing to the common-mode voltage (zero voltage), brought about in particular by a converter due to the principle involved, in the traction motor and the sudden changes in voltage at the terminals of the traction motor, of capacitive currents and arc discharges occur in the bearings in association with the parasitic capacitances in the traction motor and in the bearings of the traction motor.
Furthermore, operational reverse currents flow from the driver's own vehicle or from other vehicles via the bearings of the traction motor as a function of the selected grounding concept of the vehicle with an electric drive. This also causes damage to the bearings and to the lubricant and thus leads to premature failure of the bearings.
In order to avoid such damage to the bearings, electrically insulated bearings or insulated bearing bushings are used. Using insulated bearings or insulated bearing bushings prevents the classic wave voltages, low-frequency or DC operating currents and in particular capacitive bearing currents and arc discharges in the bearing which are due to the converter are reduced.
The disadvantage here is that the insulated bearings have a very high purchase value and require relatively sensitive installation in the drive so that the bearing insulation is not damaged. This can be confirmed by additionally checking the insulation after installation.
JP 001309505 describes a traction motor which is rigidly or permanently grounded. A capacitor merely reduces the interference currents of the vehicle with an electric drive.
JP 62114401 also has rigid grounding of the traction motor. The interference currents of the vehicle with an electric drive are returned to the source along the shortest path by means of capacitors.